This invention relates to a warp knit fabric having unidirectional stretch and recovery properties and to a method for manufacturing that fabric. More particularly, this invention relates to a warp knit fabric having ravel resistant laid-in elastic yarns.
Many warp knit fabrics with unidirectional stretch characteristics currently on the market suffer from the problem that elastic yarns or threads in the fabric easily unravel or withdraw from the fabric, for example, upon a cutting of the fabric during manufacturing operations. Such fabrics frequently have elastic yarns of spandex and are knitted on a Raschel knitting machine. A first bar of the knitting machine is generally fully threaded with aninelastic yarn and cooperates with the needles of the Raschel machine to knit the inelastic yarns. A second bar of the Raschel machine is fully threaded with spandex yarns and operates to lay those elastic yarns into the knitted structure of the inelastic yarns.
Several methods for producing a warp knit fabric having unidirectional stretch characteristics have been specifically developed for ensuring that the threads of the fabric are ravel resistant when the fabric is cut. For example, U.S. Pat. No. 4,100,770 to Titone discloses a warp knit fabric in which each wale is formed by a plurality of yarns each having alternating knitted and laid in portions, the knitting and laying of one yard being out of phase with the knitting and the laying in of another yarn. The wales are interconnected by inelastic yarn to form the fabric. Pursuant to the teachings of U.S. Pat. No. 4,244,199 to Rhode, an elastic warp knit fabric has a relatively stiff monofilament inlaid in the fabric between the courses thereof so that reverse portions of the monofilament do not extend to the outer extremities of the fabric. A skirt is provided on one side of the fabric to reduce the likelihood that the monofilament is severed when being connected for use as a waste band for a body conforming garment.
Other patents disclosing warp knit stretch fabrics include U.S. Pat. No. 4,052,866 to Saunders, U.S. Pat. No. 3,448,595 to Baltzer et al., U.S. Pat. No. 1,715,482 to Vorck and U.S. Pat. No. 4,240,160 to Imboden et al. Saunders specifically shows and describes a warp knit fabric comprising chain stitches of inelastic yarn with elastomer yarn laid into each course of the fabric to provide it with unidirectional stretch, substantially inextensible yarn being laid lengthwise in the chain stitches to limit the stretch of the fabric in the direction of the chain stitches. Baltzer et al. relates to a warp knit fabric for bandages and discloses a fabric having wales formed by knitted chains along which thick, highly twisted threads are inlaid, further inlaid yarns each traversing a pair of wales. Vorck discloses a knitted fabric in which rubber strands are firmly bound against removal.
U.S. Pat. No. 4,096,609 to Sayre and U.S. Pat. No. 3,708,836 to Frolich et al. each disclose heat setting or thermofixation of a stretchable warp knit fabric for stabilizing the same. Frolich et al. in particular is directed to a pair of tapes separably fastened to one another, each tape comprising a series of warp chains in which a plurality of yarns have been inlaid in parallel to one another. Sayre discloses the warp knitting of elastic and inelastic yarn into a longitudinally stretchable fabric having warp knitted selvedge along each edge of the fabric for limiting the longitudinal stretchability during heat setting.
An object of the present invention is to provide an improved warp knit fabric of the above-described type and a method for producing the same.
Another, more particular, object of the present invention is to provide such a fabric in which the likelihood of withdrawal of elastic yarns from the fabric is substantially reduced or eliminated.
A concomitant object of the present invention is to provide a method for producing an improved fabric wherein the unraveling of elastic yarns in the fabric is substantially prevented.
A further particular object of the present invention is to provide such a method which can be easily incorporated in the production of conventional warp knit fabrics having unidirectional stretch characteristics, particularly Raschel spandex fabrics.